1. Field of the Invention
The present invention relates to the use of a slurry of a metal oxide in processes that require mineral oxides or hydroxides. More particularly, the invention relates to methods for introducing a metal oxide slurry, such as magnesium oxide slurry or calcium oxide slurry, into an industrial process that allows the oxide to be used in the process as a source of alkalinity. The invention also relates to an apparatus for making and introducing a mineral oxide slurry into such a process.
2. Description of the Background Art
Mineral oxides and hydroxides (e.g. minerals containing various metal oxides (or hydroxides)) are frequently used in industrial processes. For example, magnesium and calcium compounds, such as their oxides and hydroxides, are used extensively in the power, mining, water treatment, paper and pulp, petro-chemical, agricultural and pollution control industries. In most instances, such mineral oxide and hydroxide compounds are used as a source of alkalinity in acid neutralization systems and for adjusting the pH in a process.
Processed mineral oxides are generally 30 to 60% less expensive on a delivered equivalency basis than their hydroxide form. For example, pound for pound, magnesium oxide powder is nearly three times more effective than magnesium hydroxide slurry. Moreover, because of the greater volume and weight of an equivalent amount of hydroxide slurry, transportation and handling costs for materials in the dry oxide form are substantially lower than for the hydroxide slurry. A dry mineral hydroxide, on the other hand, is more expensive than the mineral oxide because of the additional cost of removing water after manufacture of the mineral hydroxide.
On the other hand, material handling problems associated with the dry oxide such as bridging, dust control, plugging, abrasion and equipment reliability cause high overall operating costs when such dry oxide reagents are used. In consequence of such material handling difficulties for dry mineral oxides, the direct introduction of dry oxides into industrial, agricultural and environmental processes is limited. In the prior art, dry mineral oxides, which are sometimes delivered to a user to reduce the transportation costs associated with the hydroxide slurry, are then mixed with water by the user to hydrate the oxide. The hydroxide, in slurry form, is then introduced into the process being performed. This avoids some of the aforementioned material handling problems.
The addition of water or an aqueous solution to mineral oxides, however, produces an exothermic hydration reaction known commonly as slaking. Reactive mineral oxides undergo strong exothermic hydration when they are mixed with water. During such hydration, the reacting mixture of mineral oxide and water becomes viscous and hot. Consequently, the hydration reaction needs working through, which requires slaking equipment, e.g. high horsepower mixing equipment, an auxiliary heat source for faster initiation of hydration, safety equipment for operators, and the like. Slaking equipment is expensive and maintenance intensive. Further, the hot viscous mixture produced during slaking can be dangerous to operating personnel.
Accordingly, each of the methods presently used for introducing a mineral oxide or hydroxide into an industrial process suffers from at least one of the foregoing drawbacks. There is, therefore, a need for a more cost effective and reliable method for introducing mineral oxide powders, such as magnesium oxide powder and calcium oxide powder, into process applications.
While equipment is available for mixing and pumping cements, to applicants' knowledge no such equipment has been used for delivering mineral oxide slurry for reaction in further industrial processes in accordance with the present invention.